LAUSR

Abstract Concrete-filled steel tubes (CFSTs), which are commonly utilised as columns, can also potentially be used as structural elements which resist purely flexural loads. Previous experimental studies of CFSTs in flexure have been carried out primarily for specimens for which either longitudinally welded tubes or seamless tubes were used. Spiral-welded tubes (SWTs), which are fabricated by helically bending a continuous length of steel plate and welding the resulting abutting edges, offer several advantages compared to other tube types. However, unlike for CFSTs of other tube types, the pure flexural behaviour of such concrete-filled SWTs (CF-SWSTs) has not been investigated previously in detail. An experimental programme consisting of twelve mild-steel self-compacting CF-SWST bending tests was formulated to address this research gap. Nominal outside diameter to thickness ratios in the range 51 to 114.5 and concrete grades 20 MPa and 50 MPa were considered for the tests. All the tested CF-SWSTs displayed monotonically increasing moment deformation behaviour. It was found that existing CFST design standards provide significantly conservative estimates of the experimentally obtained capacities. The experimental behaviour of the tested CF-SWSTs was found to be equivalent to previously reported comparable CFST tests of other tube types in terms of ductility, actual to predicted moment capacity ratio and ultimate limit state deformation mode. The existence of non-uniform concrete confinement in the compressive region of the CF-SWST section was also verified through the tests. The study provided experimental evidence that SWTs can be used as direct replacements of other tube types in CFSTs designed for pure flexural loading.